Project Summary/Abstract Shiga toxin producing E. coli (STEC), including O157:H7, are a leading cause of food-borne illnesses, causing about 100,000 cases of watery and bloody diarrhea annually in the US. About 10% of cases progress to the life-threatening complication, hemolytic uremic syndrome (HUS). For reasons that are not clear, young children are more likely to develop HUS than adults, and HUS is the most common cause of acute kidney failure in children. Currently there is no treatment for STEC. Furthermore, antibiotics induce STEC to produce higher quantities of Shiga toxin, and antibiotic treatment is associated with increased incidence of severe disease. A serious limitation has been the lack of good animal models. Mice are not susceptible to STEC or Shiga toxin when introduced into the intestinal tract. We have now shown that stem cell derived ?induced human intestinal organoids? (iHIOs) are sensitive to E. coli O157:H7 and Shiga toxin, and thus represents the first tractable model system to study human disease. This proposal will test the hypotheses that iHIOs can be used to identify microbial and host factors that influence infection by STEC: Aim 1 will test role of antibiotics in preventing or enhancing disease. Aim 2 will examine the role of the microbiome in influencing disease progression. Aim 3 will determine if agents reported to down-regulate O157:H7 virulence factor expression can impact disease outcome by preventing intestinal damage. These studies will increase our understanding of human STEC infection and could provide a simple experimental system to assess potential therapeutic interventions for safety and efficacy in humans.